Spectable frames, unalterable at different temperatures and the process for making them

ABSTRACT

Spectacle frames having one or more components such as a bridge, nose rests and ear pieces of martensitic NiTi, NiTi nobium, NiTi iron alloy made by means of plastic deformation starting from a 20% work hardening raised by hammering up to 50% so that the final section of the material so treated maintains, within a range of temperatures from −50° C. to +70° C., sufficient elasticity and flexibility for adaptating the frames to the different facial forms of users.

BACKGROUND OF THE INVENTION

The invention concerns metal frames for spectacles.

FIELD OF THE INVENTION

Presently used techniques for making spectacle frames of NiTi alloyswith a memorized shape, give the alloy a mild work-hardening treatmentto facilitate processing, followed by heat treatment to memorize theshape and then further work-hardening to confer characteristics ofelasticity in the range of temperatures at which the frames will beused, from −20° C. to +40° C.

A high rate of work-hardening would make the material fragile and itwould then be impossible to obtain the complex forms needed for thespectacle frame components.

The above range of temperatures is in actual fact entirely inadequate.In very cold countries a temperature of −20° C. is normal and, generallyspeaking, in mountainous areas temperatures lower than −20° C. can bequite usual.

At 0° C. the NiTi alloy is already less rigid and loses muchconsistency. At a lower temperature the spectacle frames can be benteven with very little pressure.

On account of the memorized shape and extreme elasticity, difficultiesare encountered in adapting the frames to the faces of different users.Purpose of this invention is to overcome the above drawbacks and providefurther considerable advantages as will now be explained.

Subject of the invention are spectacle frames having one or morecomponents, such as the bridge, nose rests and ear pieces made of workhardened martenistic NiTi, NiTi niobium, NiTi iron alloys.

BRIEF SUMMARY OF THE INVENTION

The components are made by plastic deformation starting from a 20%work-hardening of the alloy and then by hammering to reach about 50%making the ultimate section of the material, so stretched, sufficientlyelastic and flexible, at temperatures ranging from −50° C. to +70° C.,to make the frames adaptable to the different faces of users.

DETAILED DESCRIPTION OF THE INVENTION

The shape is given by plastic deformation; this involves usingmechanical means to impress folds in the material, cooling it before theoperation and keeping it at a constant temperature so that the foldsbecome even.

In one advantageous type the titanium content of the alloy is between 43and 47% by weight.

Said components are connected to the other parts of the spectacles bybushes fitted into the ends of said components.

The bushes are preferably of steel.

To check the effects and advantages of this process, tests were made inItaly by the National Research Council (CNR) at its institute of MetalTechnology at Lecco.

During these tests great attention was paid to checking, at differenttemperatures, the mechanical properties of the ear pieces of the frames,comparing those available on the Italian market, the main feature ofthese ear pieces being their great elasticity.

Special care was taken in comparing:

an ear piece made by Optigen using the process here invented,

an ear piece on sale in the market made by the firm Heschenback.

The samples had uniform cross sections of about 1.2 mm in diameter.Diameters in actual fact were: Optigen 1.19 mm, Heschenback 1.27 mm. Thesurface layer was removed in a mild chemical bath.

Mechanical tests were made on the material using an MTS M/2 machinecomprising a personal computer for checking the instruments and foracquiring data by means of specific software.

Tests were made at +50° C., +30° C., 0° C., −20° C., −40° C.

Each cycle consisted, for each charge, in checking stress up to 5%, andconsequent release, in checking deformation to a value of “0”.

This made possible an evaluation of residual stress after deformationavoiding overcompression of the ear piece.

After each test the sample was removed from the press and allowed torevert to residual deformation heating it up to about 80° C.

In this way the initial configuration could be fully recovered for thesubsequent tests.

A comparison of the stress-deformation curves at 30°. for both samplesshows a marked overall elasticity though there is a great-difference inthe stress-deformation curve.

Behaviour of both samples shows a marked overall elasticity though thereis a great difference in the stress-deformation curve, The Heschenbackear piece shows a certain recovery due to memory after deformation.

Behaviour of the Optigen sample is typically superelastic maintainingits plastic deformation.

In other words there is no evidence of martensitic transformation andrelated pseudoelastic behaviour.

When the stress-deformation curves of the same samples, at a temperatureof −40° C., is compared, The behavior of the Heschenback sample istypical of a partially annealed material with marked recovery of imposeddeformation but with residual pseudoplastic deformation.

Behaviour of the Heschenback sample is typical of a partially annealedmaterial with marked recovery of imposed deformation but with residualpseudoplastic deformation.

This deformation may be easily recovered by simply heating the sample.After deformation the sample recovers its memorized shape.

Behaviour of the Optigen sample, on the other hand, is fullysuperelastic without any signs of martensitic transformation andpseudoplasticity. Residual plastic deformation of this sample is slight.

These initial results clearly show the entirely different behaviour ofthe two sample.

Both exhibit overall macroscopic elasticity and, after receiving a 5%deformation, can almost completely recover their initial shape. But thereason for this is totally different for the two arms.

Behaviour of the Heschenback sample is that of high elasticity combinedwith martensitic transformation; this takes place under stress in theshape-memorized NiTi alloys, is highly sensitive to temperature changesand ensures a low degree of tension in a wide range of deformations.

The Optigen product uses a different property of the NiTi alloy, namelyits superelasticity.

The invention offers evident advantages.

The process produces spectacle frames that, without losing theirelasticity, can be safely used at a much wider range of temperaturesthan can be obtained with other known processes, said frames beingtherefore utilizable at the temperatures prevailing in particularly coldcountries or at high altitudes, including contact by the wearer withsnow and ice.

Even at such low temperatures the frames maintain the characteristics ofhigh flexibility and resistance for which they were chosen.

This has been unquestionably proved by tests carried out in CNRlaboratories, at temperatures ranging from −20° C. to −40° C.; thesetests prove that, even subsequent to that mechanical plastic deformationneeded for making the component parts of the spectacles, the treatedmaterial always maintains its typically elastic properties.

Processes already known can produce frames which, using the same rangeof temperatures as indicated above, from −20° C. to −40° C., presentplastic behaviour while maintaining their deformation.

It may also be noted that spectacle frames do not need to besuperelastic since they are unlikely to encounter particularly highstresses in normal conditions of use.

On the other hand it must be possible to modify the ear pieces and/orthe bridge to adapt them to the user's facial form.

In conclusion, a comparison between the frames produced by the aboveprocess and those made by others at present in use, shows that, thoughless elastic, these frames are always flexible enough to withstandstresses that would be sufficient to break them had they been made usingpresently-known processes; in addition, their characteristics remainunaltered at the different temperatures at which they are used, whilethey can be adapted to fit different facial forms and, once made, thisadaption becomes stabilized.

What is claimed is:
 1. A process for making spectacle frame componentsfrom martensitic alloys selected from the group consisting of NiTi, NiTiniobium and NiTi iron, said process comprising the steps of: subjectingsaid martensitic alloys to a first plastic deformation operation with a20% work hardening method other than hammering; subjecting saidmartensitic alloys to a second plastic deformation operation with a 50%work hardening hammering method; causing said spectacle frame componentsto have sufficient elasticity and flexibility at temperatures of from−50° C. to 70° C. to allow said components to adapt to a user's facialshape.
 2. The process for making spectacle frame components as definedin claim 1, wherein the martensitic alloy comprises between 43 and 47%by weight of titanium.
 3. The process for making spectacle framecomponents as defined in claim 1, wherein the components have bushesfitted into ends of said components for connection of the components. 4.The process for making spectacle frame components as defined in claim 3,wherein the bushes are made of steel.
 5. A spectacle frame comprisingcomponents of work hardened martensitic alloys selected from the groupconsisting of NiTi, NiTi niobium and NiTi iron, said components havingbeen subject to plastic deformation in the work hardened state, saidcomponents having been subjected to a 20% work hardening by other thanhammering followed by a 50% work hardening with a hammering method, saidcomponents having sufficient elasticity and flexibility over atemperature range from −50° C. to 70° C. to adapt to a user's facialshape.
 6. The spectacle frame as in claim 5, wherein the titaniumcontent in the alloy is between 43 and 47% by weight.
 7. The spectacleframe as in claim 5, wherein the components have bushes fitted at theends of said components for connection of the components.
 8. Thespectacle frame as in claim 7, wherein the bushes are made of steel.